package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.store.Directory;
import org.apache.lucene.util.SetOnce;
import org.apache.lucene.util.SetOnce.AlreadySetException;

import java.io.IOException;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;

/**
 * <p>Expert: a MergePolicy determines the sequence of
 * primitive merge operations.</p>
 * 
 * <p>Whenever the segments in an index have been altered by
 * {@link IndexWriter}, either the addition of a newly
 * flushed segment, addition of many segments from
 * addIndexes* calls, or a previous merge that may now need
 * to cascade, {@link IndexWriter} invokes {@link
 * #findMerges} to give the MergePolicy a chance to pick
 * merges that are now required.  This method returns a
 * {@link MergeSpecification} instance describing the set of
 * merges that should be done, or null if no merges are
 * necessary.  When IndexWriter.forceMerge is called, it calls
 * {@link #findForcedMerges(SegmentInfos,int,Map)} and the MergePolicy should
 * then return the necessary merges.</p>
 *
 * <p>Note that the policy can return more than one merge at
 * a time.  In this case, if the writer is using {@link
 * SerialMergeScheduler}, the merges will be run
 * sequentially but if it is using {@link
 * ConcurrentMergeScheduler} they will be run concurrently.</p>
 * 
 * <p>The default MergePolicy is {@link
 * TieredMergePolicy}.</p>
 *
 * @lucene.experimental
 */

public abstract class MergePolicy implements java.io.Closeable {

    /** OneMerge provides the information necessary to perform
     *  an individual primitive merge operation, resulting in
     *  a single new segment.  The merge spec includes the
     *  subset of segments to be merged as well as whether the
     *  new segment should use the compound file format. */

    public static class OneMerge {

        SegmentInfo info; // used by IndexWriter
        boolean registerDone; // used by IndexWriter
        long mergeGen; // used by IndexWriter
        boolean isExternal; // used by IndexWriter
        int maxNumSegments = -1; // used by IndexWriter
        public long estimatedMergeBytes; // used by IndexWriter
        List<SegmentReader> readers; // used by IndexWriter
        List<SegmentReader> readerClones; // used by IndexWriter
        public final List<SegmentInfo> segments;
        public final int totalDocCount;
        boolean aborted;
        Throwable error;
        boolean paused;

        public OneMerge(List<SegmentInfo> segments) {
            if (0 == segments.size())
                throw new RuntimeException("segments must include at least one segment");
            // clone the list, as the in list may be based off original SegmentInfos and may be modified
            this.segments = new ArrayList<SegmentInfo>(segments);
            int count = 0;
            for (SegmentInfo info : segments) {
                count += info.docCount;
            }
            totalDocCount = count;
        }

        /** Record that an exception occurred while executing
         *  this merge */
        synchronized void setException(Throwable error) {
            this.error = error;
        }

        /** Retrieve previous exception set by {@link
         *  #setException}. */
        synchronized Throwable getException() {
            return error;
        }

        /** Mark this merge as aborted.  If this is called
         *  before the merge is committed then the merge will
         *  not be committed. */
        synchronized void abort() {
            aborted = true;
            notifyAll();
        }

        /** Returns true if this merge was aborted. */
        synchronized boolean isAborted() {
            return aborted;
        }

        synchronized void checkAborted(Directory dir) throws MergeAbortedException {
            if (aborted) {
                throw new MergeAbortedException("merge is aborted: " + segString(dir));
            }

            while (paused) {
                try {
                    // In theory we could wait() indefinitely, but we
                    // do 1000 msec, defensively
                    wait(1000);
                } catch (InterruptedException ie) {
                    throw new RuntimeException(ie);
                }
                if (aborted) {
                    throw new MergeAbortedException("merge is aborted: " + segString(dir));
                }
            }
        }

        synchronized public void setPause(boolean paused) {
            this.paused = paused;
            if (!paused) {
                // Wakeup merge thread, if it's waiting
                notifyAll();
            }
        }

        synchronized public boolean getPause() {
            return paused;
        }

        public String segString(Directory dir) {
            StringBuilder b = new StringBuilder();
            final int numSegments = segments.size();
            for (int i = 0; i < numSegments; i++) {
                if (i > 0)
                    b.append(' ');
                b.append(segments.get(i).toString(dir, 0));
            }
            if (info != null)
                b.append(" into ").append(info.name);
            if (maxNumSegments != -1)
                b.append(" [maxNumSegments=" + maxNumSegments + "]");
            if (aborted) {
                b.append(" [ABORTED]");
            }
            return b.toString();
        }

        /**
         * Returns the total size in bytes of this merge. Note that this does not
         * indicate the size of the merged segment, but the input total size.
         * */
        public long totalBytesSize() throws IOException {
            long total = 0;
            for (SegmentInfo info : segments) {
                total += info.sizeInBytes(true);
            }
            return total;
        }

        /**
         * Returns the total number of documents that are included with this merge.
         * Note that this does not indicate the number of documents after the merge.
         * */
        public int totalNumDocs() throws IOException {
            int total = 0;
            for (SegmentInfo info : segments) {
                total += info.docCount;
            }
            return total;
        }
    }

    /**
     * A MergeSpecification instance provides the information
     * necessary to perform multiple merges.  It simply
     * contains a list of {@link OneMerge} instances.
     */

    public static class MergeSpecification {

        /**
         * The subset of segments to be included in the primitive merge.
         */

        public final List<OneMerge> merges = new ArrayList<OneMerge>();

        public void add(OneMerge merge) {
            merges.add(merge);
        }

        public String segString(Directory dir) {
            StringBuilder b = new StringBuilder();
            b.append("MergeSpec:\n");
            final int count = merges.size();
            for (int i = 0; i < count; i++)
                b.append("  ").append(1 + i).append(": ").append(merges.get(i).segString(dir));
            return b.toString();
        }
    }

    /** Exception thrown if there are any problems while
     *  executing a merge. */
    public static class MergeException extends RuntimeException {
        private Directory dir;

        public MergeException(String message, Directory dir) {
            super(message);
            this.dir = dir;
        }

        public MergeException(Throwable exc, Directory dir) {
            super(exc);
            this.dir = dir;
        }

        /** Returns the {@link Directory} of the index that hit
         *  the exception. */
        public Directory getDirectory() {
            return dir;
        }
    }

    public static class MergeAbortedException extends IOException {
        public MergeAbortedException() {
            super("merge is aborted");
        }

        public MergeAbortedException(String message) {
            super(message);
        }
    }

    protected final SetOnce<IndexWriter> writer;

    /**
     * Creates a new merge policy instance. Note that if you intend to use it
     * without passing it to {@link IndexWriter}, you should call
     * {@link #setIndexWriter(IndexWriter)}.
     */
    public MergePolicy() {
        writer = new SetOnce<IndexWriter>();
    }

    /**
     * Sets the {@link IndexWriter} to use by this merge policy. This method is
     * allowed to be called only once, and is usually set by IndexWriter. If it is
     * called more than once, {@link AlreadySetException} is thrown.
     * 
     * @see SetOnce
     */
    public void setIndexWriter(IndexWriter writer) {
        this.writer.set(writer);
    }

    /**
     * Determine what set of merge operations are now necessary on the index.
     * {@link IndexWriter} calls this whenever there is a change to the segments.
     * This call is always synchronized on the {@link IndexWriter} instance so
     * only one thread at a time will call this method.
     * 
     * @param segmentInfos
     *          the total set of segments in the index
     */
    public abstract MergeSpecification findMerges(SegmentInfos segmentInfos) throws CorruptIndexException, IOException;

    /**
     * Determine what set of merge operations is necessary in
     * order to merge to <= the specified segment count. {@link IndexWriter} calls this when its
     * {@link IndexWriter#forceMerge} method is called. This call is always
     * synchronized on the {@link IndexWriter} instance so only one thread at a
     * time will call this method.
     * 
     * @param segmentInfos
     *          the total set of segments in the index
     * @param maxSegmentCount
     *          requested maximum number of segments in the index (currently this
     *          is always 1)
     * @param segmentsToMerge
     *          contains the specific SegmentInfo instances that must be merged
     *          away. This may be a subset of all
     *          SegmentInfos.  If the value is True for a
     *          given SegmentInfo, that means this segment was
     *          an original segment present in the
     *          to-be-merged index; else, it was a segment
     *          produced by a cascaded merge.
     */
    public abstract MergeSpecification findForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount, Map<SegmentInfo, Boolean> segmentsToMerge) throws CorruptIndexException, IOException;

    /**
     * Determine what set of merge operations is necessary in order to expunge all
     * deletes from the index.
     * 
     * @param segmentInfos
     *          the total set of segments in the index
     */
    public abstract MergeSpecification findForcedDeletesMerges(SegmentInfos segmentInfos) throws CorruptIndexException, IOException;

    /**
     * Release all resources for the policy.
     */
    public abstract void close();

    /** Returns true if a new segment (regardless of its origin) should use the compound file format. */
    public abstract boolean useCompoundFile(SegmentInfos segments, SegmentInfo newSegment) throws IOException;
}
